Coatings are often applied in multiple layers that may include, for instance, one or more primer layers and one or more topcoat layers. Topcoats may be used to provide color and other aesthetic properties. Topcoats commonly are applied as either one layer as a color coat, for example the well-known acrylic enamels, or in two layers as a color coat with a clear overcoat. Color-plus-clear composite coatings are widely used, especially in the automotive industry, because of their exceptional appearance. Automotive coatings requirements are particularly stringent. Automotive coatings must not only have the desirable appearance properties of high gloss, depth of color, distinctiveness of image, and so on. Topcoats must also be resistant to marring, scratching, etching or spotting from environmental depositions, chalking, and other forms of film degradation. In a color-plus-clear composite coating, it is particularly critical to have a clearcoat that is resistant to film degradation.
Rehfuss et al. disclose in U.S. Pat. Nos. 5,356,669 and 5,474,811, the disclosure of which is incorporated herein by reference, clearcoat compositions comprising carbamate-functional polymers that may be cured by reaction with compounds having a plurality of carbamate-reactive groups.
Carbamate-functional reactive diluents are described in WO 87/00851, Hoy et al.; U.S. Pat. No. 5,115,015, Richey, Jr., et al.; U.S. Pat. No. 4,814,382, Hoy et al.; U.S. Pat. No. 4,677,168, Hoy et al.; and U.S. Pat. No. 4,520,167, Blank et al., the disclosures of which are incorporated herein by reference. The carbamate-functional reactive diluents are low molecular weight compounds with one carbamate group. Because of their monofunctionality, such compounds cannot be used as crosslinking agents in coating compositions.
Di-carbamate-functional crossinking agents based upon a carbamate functional polymers are disclosed in Rehfuss, U.S. Pat. No. 5,373,069, the disclosure of which is incorporated herein by reference.
Tri-carbamate-functional crosslinking agents based upon isocyanurate-type materials are disclosed in Rehfuss, U.S. Pat. No. 5,336,566, the disclosure of which is incorporated herein by reference. These materials have a cyanuric ring nucleus and three primary carbamate terminal groups.
Alkoxycarbonylamino-1,3,5-triazine crosslinking agents are disclosed in U.S. Pat. No. 4,939,213; U.S. Pat. No. 5,084,541; U.S Pat. No. 5,288,865; Kuang et al., WO 96/15185; Flood et al., WO 96/04258; Bay, WO 96/11915; and Flood et al., EP 0 624 577, the disclosures of which are incorporated herein by reference. The crosslinking agent described in these references have secondary carbamate groups on the amino group that react with alcohols or other active hydrogen-containing materials. The mechanism for the reaction is thought to involve loss of alcohol from the carbamate crosslinking agent and then formation of a urethane bond with the active hydrogen-containing material.
It has now been discovered that carbamate-functional crosslinking agents can be synthesized based upon polyfunctional amino compounds. The compositions of the present invention include primary or secondary carbamate-functional crosslinking agents based upon polyfunctional amino compounds in combination with binder resins, such as addition polymers, or aminoplast resins and materials that have at least two groups reactive with carbamate functionality. The coatings formed from the compositions of the present invention have crosslinked networks with urethane linkages. These linkages have been shown to be durable, and environmental etch-resistant, as discussed in Rehfuss et al. disclose in U.S. Pat. Nos. 5,356,669 and 5,474,811.